Introduction

• Cause: caused in the UK by Ovine Herpes Virus-2 (OHV2) and in Africa by Alcephaline Herpes Virus-1 (AlHV-1), for which wildebeest are the reservoir.
• Signs: acute onset illness with depression, anorexia, pyrexia and oculo-nasal discharge.
• Diagnosis: history of sheep contact, characteristic clinical signs and confirmation by PCR.
• Treatment: euthanasia, on welfare grounds.
• Prognosis: extremely poor (chronic cases have been reported that survive > 800 days).

Pathogenesis

Etiology

• Caused in the UK by Ovine Herpes Virus-2 (OHV2), for which sheep are the reservoir.
• It is a major limitation to cattle farming in parts of Africa, where it is caused by Alcephaline Herpes Virus-1 (AlHV-1), for which wildebeest are the reservoir.

Predisposing factors

General

• Housing cattle and sheep together is a major risk factor.

Pathophysiology

• A study of MCF lesions in 11 beef cattle surviving for between 39 and >800 days identified the following lesions:
  • Subacute-chronic MCF (5 cows examined):
    • All examined cows showed signs of ophthalmitis, including: stromal keratitis, uveitis and retinitis .
    • All examined cows had erosions of the proximal GIT and encephalitis. 3/5 cows also had erosions of the distal GIT.
    • All examined cows had arteriopathic lesions. Arteriosclerosis was the most consistent lesion, whilst lymphoid vasculitis and fibrinoid necrosis were less consistent.
    • Other lesions found include: necrotising dermatitis, serous fat atrophy, lymphadenopathy, unilateral perforating keratitis, unilateral iridial prolapse, acute necrotic splenitis and bilateral pigmentary keratitis.
• MCF with recovery (5 cows examined):
  • All examined cows showed signs of arteriosclerosis, whilst lymphoid vasculitis was less consistent. None of the cows suffered from fibrinoid necrosis.
  • All examined cows suffered from ophthalmitis, with stromal keratitis the most consistent finding. Uveitis and retinitis were present in 4/5 animals.
  • 4/5 cows had proximal GIT ulceration and encephalitis, however only one had distal GIT ulceration.
  • Other lesions found include: unilateral perforating keratitis, unilateral iridial prolapse, atrophy of seminiferous tubules, severe bilateral pigmentary keratitis and atrophy in ovarian follicles.

Epidemiology

• MCF is a relatively rare, sporadic disease in the UK affecting cattle and deer.
• Outbreaks can occur, but usually only a single case is seen.
• Contact with sheep or goats (especially around lambing) seems to be necessary for transmission of the disease to cattle.
• There are high rates of seropositivity in sheep, but the route of transmission is unknown.
• Cases of MCF may occur months after contact with sheep, suggesting prolonged incubation or latent infection.
• The virus is very fragile and will not survive for more than a day outside the host.
• Cattle are considered ‘dead - end’ hosts and are not thought to transmit MCF.

Diagnosis

Treatment

Prevention